The problem im having with my 1996 Silverado with 96,000 miles, the other day the heater quit blowing hot air and when I change the control postion the dash or any position it will only blow cold air through the defrost vents, the blower control (hi-lo) still works.
Any help would be greatly appreciated since it is winter and cold.
Look for a broken vacuum hose. This will allow the air flow to be distibuted to the vents, floor, etc. The cold air could result in, the thermostat being stuck open, the blender door not moving, or the heater core being plugged up. Let me know, and good luck : )